Secure starting of an electronic circuit

ABSTRACT

A method of checking the authenticity of at least a first portion of the content of a non-volatile memory of an electronic device including a microcontroller and an embedded secure element is disclosed. The method includes starting the microcontroller with instructions stored in a first secure memory area associated with the microcontroller and starting the secure element. The secure element has a plurality of decipher keys, each associated with a portion of the content of a second reprogrammable non-volatile memory area associated with the microcontroller. The secure element performs a signature check on a first portion of the content of the second area. If the signature is verified, the secure element sends the decipher key associated with the first portion to the microcontroller. If the signature is not verified, the secure element executes a signature check on another portion of the content of the second memory area.

BACKGROUND Technical Field

The present disclosure generally relates to electronic circuits and,more particularly, to devices comprising a processor and an embeddedsecure element. The present disclosure more particularly applies tocontrolling the authenticity of all or part of a code or of firmwarecomprising a set of instructions executed by the processor at thestarting of the device.

Description of the Related Art

Many electronic devices, for example, cell phones, electronic keys(dongles), etc., are equipped with microprocessors for processing dataand executing various applications. Among such applications, some arenow associated with operations requiring preserving the security of theexchanged data, for example, payment, access control operations, etc.

Larger devices, for example, computers, video decoding boxes (Set TopBox), etc., comprise trusted platform modules (TPM) which enable toprotect the content of instruction memories and in particular to checkthat a code or program to be executed has not been corrupted. Suchmodules are lacking in less elaborate devices such as, for example, cellphones, electronic keys, and connected objects (connected watch, accessdongle, etc.).

Electronic devices, even if they comprise no secure platform module, arehowever more and more often equipped with embedded secure elements,which actually are integrated circuits representing the securityfunctions of microcircuit cards (smartcard, SIM, etc.). For example,such secure elements may contain the microcircuit card emulationapplication which provides the security authentication service forpayment, access control, etc., operations.

BRIEF SUMMARY

An embodiment facilitates securing the starting of an electronic deviceto control that the code or the data that it contains are authentic ornon-corrupted.

An embodiment facilitates the starting of an electronic device capableof implementing a plurality of operating systems to control and/ormanage which operating system has been started.

An embodiment facilitates securing the starting of an electronic devicecapable of implementing a plurality of operating systems to controlwhether the code or the data associated with the operating system thatit implements are authentic or non-corrupted.

An embodiment provides protecting an embedded secure element associatedwith a microprocessor in an electronic device.

An embodiment provides a method of checking the authenticity of at leasta first portion of the content of a non-volatile memory of an electronicdevice comprising a microcontroller and an embedded secure element,comprising the steps of:

-   -   starting the microcontroller with instructions stored in a first        secure memory area associated with the microcontroller;    -   starting the secure element, the secure element comprising a        plurality of decipher keys, each associated with the content of        a second reprogrammable non-volatile memory area associated with        the microcontroller;    -   executing, with the secure element, a signature check on a first        portion of the content of the second area;    -   if the signature is verified, the secure element sends the        decipher key associated with said first portion to the        microcontroller; and    -   if the signature is not verified, the secure element executes a        signature check on another portion of the content of said second        memory area.

According to an embodiment, each portion of the content of the secondnon-volatile memory area comprises data and instructions enabling themicrocontroller to implement a different operating system.

According to an embodiment, the microcontroller is capable ofimplementing at least three operating systems.

According to an embodiment, if no signature is verified, the secureelement sends data to the microcontroller.

According to an embodiment, said data comprise a decipher key capable ofdeciphering no portion of the content of said second non-volatile memoryarea.

According to an embodiment, said data comprise data and instructionsenabling the microcontroller to implement a new operating system, suchas an operating system not previously stored in the memory of themicrocontroller.

According to an embodiment, said new operating system is an operatingsystem enabling to:

-   -   restart the microcontroller;    -   initiate a diagnosis of the microcontroller;    -   update one or a plurality of operating systems that the        microcontroller is capable of implementing; or    -   reset the microcontroller.

According to an embodiment, the microcontroller generates a second key,transmits it to the secure element which uses it to cipher thetransmission of the first key to the microcontroller.

According to an embodiment, the transmission of the second key uses apublic key asymmetric algorithm.

According to an embodiment, the asymmetric cipher key is unique permicrocontroller/secure element pair.

According to an embodiment, the first key is not stored in thenon-volatile memory in the microcontroller.

According to an embodiment, in case of an authentic update of at least aportion of the content of the second area, the signature associated withsaid portion stored in the secure element is accordingly modified.

According to an embodiment, the first key is generated by the secureelement.

According to an embodiment, if the signature is not verified, the secureelement selects another portion of the content of said second memoryarea that it checks.

According to an embodiment, the secure element may select anotherportion of the content of said second memory area based on aninstruction received during a previous implementation of a portion ofthe content of the second memory area.

Another embodiment provides an electronic device comprising:

-   -   a microcontroller; and    -   an embedded secure element,        the microcontroller and the secure element being capable of        implementing one or more of the methods disclosed herein.

According to an embodiment, one or more intermediate circuits areinterposed between the microcontroller and the secure element.

In an embodiment, a method comprises: starting a microcontroller of anelectronic device with instructions stored in a first secure memory areaassociated with the microcontroller; starting a secure element of theelectronic device, the secure element having a plurality of decipherkeys, each associated with a portion of a plurality of portions ofcontent of a second reprogrammable non-volatile memory area associatedwith the microcontroller; executing, with the secure element, asignature check on a first portion of the plurality of portions ofcontent of the second area; in response to the signature check verifyingthe first portion of the content of the second area, sending, by thesecure element, the decipher key associated with the first portion tothe microcontroller; and in response to the signature check notverifying the first portion of the content of the second area,executing, by the secure element, a signature check of another portionof the plurality of portions of content of the second memory area. In anembodiment, each portion of the plurality of portions of content of thesecond memory area stores data and instructions to implement arespective one of a plurality of operating systems. In an embodiment,the plurality of portions of the second memory area comprise three ormore portions. In an embodiment, the method comprises responding, by thesecure element, to a failure of verification of each of the plurality ofportions by sending data to the microcontroller. In an embodiment, thedata comprises a dummy decipher key. In an embodiment, the datacomprises data and instructions to cause the microcontroller toimplement an operating system other than one of the plurality ofoperating systems. In an embodiment, the operating system other than oneof the plurality of operation systems is an operating system to: restartthe microcontroller; initiate a diagnosis of the microcontroller; updateone or more of the plurality of operating systems; reset themicrocontroller; or various combinations thereof. In an embodiment, themicrocontroller generates a second key and transmits the second key tothe secure element, which uses the second key to cipher the transmissionof the first key to the microcontroller. In an embodiment, thetransmission of the second key uses a public key asymmetric algorithm.In an embodiment, an asymmetric cipher key is unique permicrocontroller/secure element pair. In an embodiment, the first key isnot stored in the non-volatile memory in the microcontroller. In anembodiment, the method comprises, in response to an authentic update ofa portion of the content of the second area, modifying the signatureassociated with the portion stored in the secure element. In anembodiment, the first key is generated by the secure element. In anembodiment, the method comprises, in response to the signature check notverifying the first portion of the content of the second area,selecting, by the secure element, the another portion of the pluralityof portions of content of the second memory area to check. In anembodiment, the secure element selects the another portion of thecontent of the second memory area based on an instruction receivedduring a previous implementation of a portion of the content of thesecond memory area.

In an embodiment, an electronic device comprises: a microcontrollerassociated with a first secure memory area and a second reprogrammablenon-volatile memory area, the second reprogrammable memory area having aplurality of portions; and an embedded secure element coupled to themicrocontroller, the embedded secure element having a plurality ofdecipher keys each associated with a respective portion of the pluralityof portions of the second reprogrammable memory area, wherein theembedded secure element, in operation: executes a signature check on afirst portion of the plurality of portions of content of the secondarea; in response to the signature check verifying the first portion ofthe content of the second area, sends the decipher key associated withthe first portion to the microcontroller; and in response to thesignature check not verifying the first portion of the content of thesecond area, executes a signature check of another portion of theplurality of portions of content of the second memory area. In anembodiment, each portion of the plurality of portions of content of thesecond non-volatile memory area stores data and instructions toimplement a respective one of a plurality of operating systems on themicrocontroller. In an embodiment, the secure element, in operation,responds to a failure of verification of each of the plurality ofportions by sending data to the microcontroller. In an embodiment, thedata comprises data and instructions to cause the microcontroller toimplement an operating system other than one of the plurality ofoperating systems. In an embodiment, the operating system other than oneof the plurality of operation systems, when executed by themicrocontroller: restarts the microcontroller; initiates a diagnosis ofthe microcontroller; updates one or more of the plurality of operatingsystems; resets the microcontroller; or various combinations thereof. Inan embodiment, the microcontroller, in operation, generates a second keyand transmits the second key to the secure element, and the secureelement, in operation, uses the second key to cipher the transmission ofthe first key to the microcontroller. In an embodiment, the transmissionof the second key uses a public key asymmetric algorithm. In anembodiment, the electronic device comprises an intermediate circuitcoupled between the microcontroller and the secure element.

In an embodiment, a system comprises: a memory; a microcontrollercoupled to the memory, the microcontroller having an associated firstsecure memory area and an associated second reprogrammable non-volatilememory area, the second reprogrammable memory area having a plurality ofportions; and an embedded secure element coupled to the microcontroller,the embedded secure element having a plurality of decipher keys eachassociated with a respective portion of the plurality of portions of thesecond reprogrammable memory area, wherein the embedded secure element,in operation: executes a signature check on a first portion of theplurality of portions of content of the second area; in response to thesignature check verifying the first portion of the content of the secondarea, sends the decipher key associated with the first portion to themicrocontroller; and in response to the signature check not verifyingthe first portion of the content of the second area, executes asignature check of another portion of the plurality of portions ofcontent of the second memory area. In an embodiment, in operation, eachportion of the plurality of portions of content of the secondnon-volatile memory area stores data and instructions to implement arespective one of a plurality of operating systems on themicrocontroller. In an embodiment, the secure element, in operation,responds to a failure of verification of each of the plurality ofportions by sending data and instructions to the cause themicrocontroller to implement an operating system other than one of theplurality of operating systems. In an embodiment, the first securememory area is integrated into the microcontroller and the secondreprogrammable memory area is integrated into the memory.

In an embodiment, a non-transitory computer-readable medium's contentswhich cause an electronic device to perform a method, the methodcomprising: starting a microcontroller of the electronic device;starting a secure element of the electronic device, the secure elementhaving a plurality of decipher keys, each associated with a portion of aplurality of portions of content of a reprogrammable non-volatile memoryarea associated with the microcontroller; executing, with the secureelement, a signature check on a first portion of the plurality ofportions of content of the reprogrammable non-volatile memory area; inresponse to the signature check verifying the first portion of thecontent, sending, by the secure element, the decipher key associatedwith the first portion to the microcontroller; and in response to thesignature check not verifying the first portion of the content,executing, by the secure element, a signature check of another portionof the plurality of portions of content. In an embodiment, each portionof the plurality of portions of content stores data and instructions toimplement a respective one of a plurality of operating systems. In anembodiment, the method comprises responding, by the secure element, to afailure of verification of each of the plurality of portions by sendingdata to the microcontroller. In an embodiment, the data comprises dataand instructions to cause the microcontroller to implement an operatingsystem other than one of the plurality of operating systems. In anembodiment, the contents comprise instructions stored in a secure memoryarea associated with the microcontroller.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing example features and advantages, as well as others, willbe described in detail in the following description of specificembodiments given by way of illustration and not limitation withreference to the accompanying drawings, in which:

FIG. 1 very schematically shows in the form of blocks an embodiment ofan electronic device equipped with a microcontroller and with a secureelement;

FIG. 2 very schematically shows in the form of blocks an embodiment of astart-up sequence of the microcontroller of the electronic device ofFIG. 1 ; and

FIG. 3 shows in the form of a flowchart another embodiment of a start-upsequence of the microcontroller of the electronic device of FIG. 1 .

DETAILED DESCRIPTION

Like features have been designated by like references in the variousfigures unless the context indicates otherwise. In particular, thestructural and/or functional features that are common among the variousembodiments may have the same references and may dispose similar oridentical structural, dimensional and material properties.

For the sake of clarity, only the steps and elements that are useful foran understanding of the embodiments described herein have beenillustrated and described in detail.

Unless indicated otherwise, when reference is made to two elementsconnected together, this signifies a direct connection without anyintermediate elements other than conductors, and when reference is madeto two elements coupled together, this signifies that these two elementscan be connected or they can be coupled via one or more other elements.

In the following disclosure, unless specified otherwise, when referenceis made to absolute positional qualifiers, such as the terms “front”,“back”, “top”, “bottom”, “left”, “right”, etc., or to relativepositional qualifiers, such as the terms “above”, “below”, “higher”,“lower”, etc., or to qualifiers of orientation, such as “horizontal”,“vertical”, etc., reference is made to the orientation shown in thefigures.

Unless specified otherwise, the expressions “around”, “approximately”,“substantially” and “in the order of” signify within 10%, or within 5%.

FIG. 1 very schematically shows, in the form of blocks, an example of anelectronic device 1 of the type to which example embodiments which willbe described may apply.

Device 1, for example, a cell phone, an electronic key, etc., comprisesa microcontroller 2 (CPU—Central Processing Unit or processing core) incharge of executing all or part of the programs and applicationsimplemented in the device. Microcontroller 2 communicates, via one or aplurality of address, data, and control buses 12, with differentelectronic circuits and peripherals (not shown) of device 1, forexample, display control circuits, of a keyboard, etc., as well as withvarious wired or wireless input-output interfaces 14 (I/O) (for example,Bluetooth). Microcontroller 2 generally integrates volatile andnon-volatile memories and also processes the content of similar memories16 (MEM (VM/NVM)) of device 1. Microcontroller 2 is capable ofimplementing a plurality of operating systems, or low-level firmware. Asan example, a first operating system may be a primary operating system,a second operating system may be an update operating system, a thirdoperating system may be a data recovery operating system. According toanother example, microcontroller 2 is capable of implementing aplurality of primary operating systems, such as for example the primaryoperating system of a telephone and the operating system of a transportcard or of a bank card. Microcontroller 2 and various circuits of device1 are powered by a power unit 18 (PU). For example, unit 18 is abattery, possibly associated with a voltage regulator.

In applications targeted by the present disclosure, device 1 comprisesan embedded secure element 3 (for example, eSE—embedded Secure elementor eUICC—embedded Universal Integrated Circuit Card) which includes asecure microprocessor or processing core. Element 3 is intended tocontain secure services or applications of the electronic device, forexample, payment, access control, and other applications.

Possibly, an intermediate element or circuit 4, for example, anear-field communication controller 4 (NFC), also called contactlessfront end (CLF), a Bluetooth controller, etc., equips device 1. Element4 (illustrated in dotted lines in FIG. 1 ) is capable of being used bymicrocontroller 2, for example by connections of twin-wire type (I2C orSPI) and, by element 3, by a connection of single-wire type (SWP—SingleWire Protocol).

According to the voltage level supported by secure element 3, saidelement is either powered by unit 18 or, as shown in FIG. 1 , by element4, which is itself powered by unit 18. For example, the case of amicrocontroller 2 and of a contactless communication controller 4,powered under a voltage in the order of 3 volts by unit 18 and of anelement 3 powered under a voltage in the order of 1.8 volt (alim) bycontroller 4 can be considered. The need for a power supply by NFCcontroller 4 may be due to the levels used by the communicationprotocols between the controller and secure element 3. According to avariant, contactless communication controller 4 is absent, secureelement 3 is, in this case, directly connected to microcontroller 2 andis directly powered by unit 18.

It is provided to take advantage of the presence of embedded secureelement 3 to manage which operating system is executed bymicrocontroller 2.

It is further provided to take advantage of the presence of embeddedsecure element 3 to check the authenticity of the content (data,instructions, etc.) of all or part of the memories associated withmicrocontroller 2. More particularly, it is provided to take advantageof the presence of secure element 3 to check the authenticity of thedata and instructions associated with each operating system capable ofbeing implemented by microcontroller 2 before its implementation.

FIG. 2 is a simplified representation illustrating an embodiment of astart-up sequence of microcontroller 2 of electronic device 1 of FIG. 1.

Risks inherent to the starting of microcontroller 2 in terms of datasecurity are that, in case of a piracy, data or instructions of theembedded secure element can be pirated. This risk occurs at the start,called cold boot, which follows a powering-on since not all themechanisms for controlling the access to the different circuits havebeen initialized yet such as, in particular, the configuration of thememories in free areas and reserved areas. The problem is not as seriousin the case of a “hot” reset of the device, that is, with nointerruption of the microcontroller power supply, since such memory areaconfiguration mechanisms are generally untouched. However, the describedembodiment may also be implemented in case of a partial or totaldeleting of the memory in a reset operation.

At a starting (powering-on of the electronic circuits of the device) ora reset with an interruption of the power supply, microcontroller 2starts by accessing a set area 51 (BOOT) of its non-volatile memorycontaining a code (a start-up program). Area 51 is generally a deadmemory area, that is, non-volatile and non-reprogrammable (sometimescalled “immutable”). According to a variant, area 51 may be a limited orrestricted secure write area of a non-volatile or volatile memory. It isthus set on manufacturing and does not risk being modified by a possiblepirate. In fact, the memory area (MEMCPU) 52 to be protected is anon-volatile memory area which will be operated by microcontroller 2, onimplementation of the operating systems. Such an area 52 generallycontains code (instructions) and data, which are reprogrammableaccording to applications. If a pirate succeeds in storing an attackcode in these areas, he/she risks being able to access secure element 3,and would then be able to modify the behavior of device 1, collectconfidential data and information directly manipulated by the operatingsystem to supply them, for example, to a pirate application implementedby the operating system. In the rest of the description, it isconsidered that area 52 of the non-volatile memory of microcontroller 2is divided into a plurality of portions, each comprising data andinstructions relative to an operating system. More particularly, thedata and instructions relative to an operating system are all cipheredwith one or a plurality of cipher keys. Each operating system has itsown cipher key(s) different from the cipher keys of the other operatingsystems.

According to an embodiment, the start-up code 51 executed by themicrocontroller contain an instruction for starting secure element 3(eSE) as well as, subsequently in the sequencing of the initializationprocess (illustrated by an arrow 53), an instruction INST for starting aprocess of checking of a portion of area 52 by element 3. Onceinstruction INST has been communicated by microcontroller 2 to element3, microcontroller 2 sets to a hold mode (HOLD) where it waits for aresponse from secure element 3. As long as it does not receive thisresponse, it does not carry on the execution of the code that itcontains. According to a variant, secure element 3 can start by itselfwhen it is powered on, for example, at the same time as microcontroller2.

The checking CHECK performed by element 3 comprises reading a firstportion of area 52 storing the data relative to a first operating systemand executing an authenticity check mechanism on said portion. Forexample, this mechanism is a signature calculation based on the code anddata contained in the first portion of area 52, for checking thissignature against a reference signature stored in element 3. In thiscase, in case of an authorized modification of the content of area 52,the reference signature stored in element 3 is updated to allowsubsequent authenticity checks.

In other words, checking CHECK comprises performing a signaturecalculation from the code and the data relative to an operating systemeach time the operating system requests being implemented. In otherwords, the checking enables to check whether the data relative to theoperating system are not corrupted.

Further, all the data relative to the operating systems are ciphered.More particularly, each set of data relative to an operating system isciphered by using at least one same cipher key different from at leastanother cipher key of another set of data relative to another operatingsystem. The corresponding decipher keys are all stored in secure element3.

If element 3 validates the authenticity of the content of the portion ofarea 52, it responds (OK) to microcontroller 2 and sends thereto thecipher key associated with the data of area 52 which have just beenchecked. Microcontroller 2 can then leave its hold mode and execute theoperating system associated with these data.

However, if element 3 does not validate (NOK) the content of the firstportion of area 52, it sends an instruction to the microcontrollerindicating that the first operating system cannot be implemented.Element 3 then requests to receive the data and instructions fromanother portion of area 52 in order to authenticate another operatingsystem. If all the operating systems of the microcontroller arecorrupted, then element 3 can send back data or an instruction to themicrocontroller, for example, a null decipher key, or a microcontrollerdefault instruction. Element 3 may further send a series of data andinstructions relative to a new operating system to microcontroller 2.According to an example, the new operating system may allow a restartingor a resetting of microcontroller 2 or of device 1. According to anotherexample, the new operating system may for example be a diagnosisoperating system enabling to perform tests on the operation of themicrocontroller or even of the complete device 1. According to stillanother example, the new operating system may be an operating system forupdating the operating systems of microcontroller 2.

FIG. 3 is a simplified representation illustrating in further detail anembodiment of the start-up sequence of the microcontroller of theelectronic device of FIG. 1 .

According to this embodiment, the method is performed by exchange ofmessages between microcontroller 2 and secure element 3.

The starting of microcontroller 2 (block 61, BOOT CPU) causes thestarting (block 62, BOOT eSE) of secure element 3. Once started, element3 waits for instructions (WAIT).

Further, the checking of the content of the different portions of area52 or of the non-volatile memory areas (NVM) containing code to bechecked is also performed, for example, by a signature check by element3.

According to an embodiment, the code and the fixed data, stored innon-volatile memory 52 and forming the initialization data ofmicrocontroller 2 after the starting thereof, are ciphered. Theciphering used is for example a symmetrical AES-type ciphering. However,instead of being stored in microcontroller 2, the cipher key(s) arestored in secure element 3.

Once microcontroller 2 has started (end of block 61) and it has given astart instruction to element 3, it generates a key (block 63, GENKeyAESRDM), for example a random number of the size of the AES used tocipher the code.

Microcontroller 2 then transmits key KeyAESRDM to the secure element.Such a transmission may be performed by a public key mechanism, themicrocontroller ciphering key KeyAESRDM with the public key of thealgorithm (block 64, CIPHER KeyAESRDM (PUBLIC KEY)). In an embodiment,microcontroller 2 does not store random number KeyAESRDM in anon-volatile memory. Indeed, it is sufficient for it to store thisnumber in a volatile memory, which decreases risks of attack. Once keyKeyAESRDM has been transmitted, the microcontroller sets to the waitingmode (WAIT).

Element 3 deciphers KeyAESRDM by means of the public key mechanism(block 65, DECIPHER KeyAESRDM)) and stores it (block 66, STOREKeyAESRDM).

Element 3 then deciphers (block 67, DECIPHER CODE (AESCodeKey) the codecontained in the portion of area 52 of the non-volatile memory ofmicrocontroller 2 (or associated therewith) relative to the operatingsystem to be implemented. Element 3 calculates and checks (block 68,COMPUTE/CHECK SIGNATURE) the signature of this code.

If the signature is correct (output Y of block 69), element 3 ciphersdecipher key AESCodeKey, corresponding to the data which have just beenchecked, with key KeyAESRDM (block 70, CIPHER AESCodeKey (KeyAESRDM))and sends it to microcontroller 2. The latter deciphers key AESCodeKey(block 71, DECIPHER AESCodeKey (PUBLIC KEY)) with key KeyAESRDM. Aspreviously mentioned, element 3 stores a plurality of decipher keysAESCodeKey, each associated with all or part of the data relative to anoperating system.

Microcontroller 2 then uses key AESCodeKey to decipher the codecontained in the portion of area 52, that is, the data which have justbeen checked by secure element 3, and to execute it (EXECUTE). However,key AESCodeKey is not stored in the non-volatile memory bymicrocontroller 2. Thus, on the side of microcontroller 2, numberKeyAESRDM and key AESCodeKey are only stored in volatile storageelements (RAM, registers, or the like).

If the signature is incorrect (output N of block 69, OK?), element 3requests to examine the next portion of area 52 (block 72, OTHER CODE?),that is, the data and instructions relative to another operating systemimplemented by microcontroller 2. Thus, the data and instructionsrelative to the first operating system are not deciphered, and thuscannot be used by microcontroller 2.

If the data and instructions relative to another operating system havenot been checked yet (output Y of block 72), then the data relative tothis other operating system are sent to element 3 (block 52) and theirsignature is checked (block 67).

If all the data and instructions relative to the other operating systemshave already been checked and are considered as corrupted (output N ofblock 72), then element 3 sends data or an instruction to themicrocontroller (block 73, SEND NULL), for example, a null decipher key,or a default instruction regarding microcontroller 2. Element 3 mayfurther send a series of data and instructions relative to a newoperating system to microcontroller 2. According to an example, the newoperating system may allow a restarting or a resetting ofmicrocontroller 2 or of device 1. According to another example, the newoperating system may for example be a diagnosis operating systemenabling to perform tests on the operation of microcontroller 2 or evenof the complete device 1.

According to still another example, the new operating system may be anoperating system for updating the operating systems of microcontroller2.

The data or instruction sent by element 3, or possibly the series ofdata and of instructions, are ciphered with key KeyAESRDM (block 70)before their sending to microcontroller 2. Microcontroller 2 deciphersthem (block 71) and then uses them.

According to an alternative embodiment, key AESCodeKey is generated bysecure element 3 for each change of signature of the code contained inarea 52, that is, each time all or part of the code is modified.

According to another variant, on manufacturing of the circuits (ofmicrocontroller 2 and of secure element 3), the cipher code of memory 52of the microcontroller is generated by secure element 3. This means thatcode AESCodeKey varies from one device 1 to another.

In an embodiment, the asymmetric key (pair of public and private key) isunique per pair of microcontroller component 2/secure element 3.

According to another variant, security element 3 may select whichoperating system is to be implemented by microcontroller 2.

According to another variant, the security element may check all theoperating systems before deciding which operating system should beimplemented.

According to another variant, on update of an operating system, thedecipher key stored in the secure element 3 which is associatedtherewith may be modified.

According to another variant, secure element 3 may be in charge ofdeciding which operating system should be implemented. It may forexample decide which operating system should be started after havingdetermined that data relative to a first operating system are corrupted.It may for example decide to start another operating system having thefunction of updating said first operating system. More particularly,secure element 3 could load another operating system capable ofimplementing the data of microcontroller 2. To make this choice, thesecure element could receive a secure instruction indicating thereto theprocedure to follow before the checking of the data, for example, duringa previous implementation of one of the operating systems. As a variant,secure element 3 could start the operating system even before thechecking of the data relative to the operating systems if it hasreceived the order during a directly previous implementation of anotheroperating system.

Various embodiments and variants have been described. Those skilled inthe art will understand that certain features of these variousembodiments and variants may be combined, and other variants will occurto those skilled in the art.

Finally, the practical implementation of the described embodiments andvariations is within the abilities of those skilled in the art based onthe functional indications given hereabove.

Such alterations, modifications, and improvements are intended to bepart of this disclosure, and are intended to be within the spirit andthe scope of the present disclosure. Accordingly, the foregoingdescription is by way of example only and is not intended to belimiting.

Some embodiments may take the form of or comprise computer programproducts. For example, according to one embodiment there is provided acomputer readable medium comprising a computer program adapted toperform one or more of the methods or functions described above. Themedium may be a physical storage medium, such as for example a Read OnlyMemory (ROM) chip, or a disk such as a Digital Versatile Disk (DVD-ROM),Compact Disk (CD-ROM), a hard disk, a memory, a network, or a portablemedia article to be read by an appropriate drive or via an appropriateconnection, including as encoded in one or more barcodes or otherrelated codes stored on one or more such computer-readable mediums andbeing readable by an appropriate reader device.

Furthermore, in some embodiments, some or all of the methods and/orfunctionality may be implemented or provided in other manners, such asat least partially in firmware and/or hardware, including, but notlimited to, one or more application-specific integrated circuits(ASICs), digital signal processors, discrete circuitry, logic gates,standard integrated circuits, controllers (e.g., by executingappropriate instructions, and including microcontrollers and/or embeddedcontrollers), field-programmable gate arrays (FPGAs), complexprogrammable logic devices (CPLDs), etc., as well as devices that employRFID technology, and various combinations thereof.

The various embodiments described above can be combined to providefurther embodiments. Aspects of the embodiments can be modified, ifnecessary to employ concepts of the various patents, applications andpublications to provide yet further embodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. A method, comprising: starting a microcontroller of an electronicdevice with instructions stored in a first memory area, wherein thefirst memory area is a secure memory area; starting a secure circuit ofthe electronic device, the secure circuit having a plurality of decipherkeys associated with respective portions of content of a second memoryarea, wherein the second memory area is a non-volatile memory area;executing, with the secure circuit, a signature check on a first portionof content of the second memory area, the first portion of contentstoring data and instructions to implement a first operating system; inresponse to the signature check verifying the first portion of content,sending, by the secure circuit, a decipher key associated with the firstportion of content to the microcontroller; and in response to thesignature check not verifying the first portion of content, executing,by the secure circuit, a signature check of a second portion of contentof the second memory area, the second portion of content storing dataand instructions to implement a second operating system.
 2. The methodaccording to claim 1, comprising: responding, by the secure circuit, toa failure of verification of a set of portions of the plurality ofportions by sending a dummy decipher key to the microcontroller.
 3. Themethod according to claim 1, comprising: responding, by the securecircuit, to a failure of verification of a set of portions of theplurality of portions by sending data and instructions to cause themicrocontroller to implement an operating system other than an operationsystem associated with a portion of the plurality of portions.
 4. Themethod according to claim 1, comprising: generating, by themicrocontroller, a second key, and transmitting the second key to theembedded secure circuit; and encrypting, by the secure circuit, thedecipher key using the second key, wherein the sending the decipher keyto the microcontroller comprises sending the encrypted decipher key tothe microcontroller.
 5. An electronic device, comprising: amicrocontroller; a first memory area couple to microcontroller, whereinthe first memory area is a secure memory area, which, in operation,stores instructions executable by the microcontroller; a second memoryarea coupled to the microcontroller; and an embedded secure circuitcoupled to the microcontroller, wherein the embedded secure circuit, inoperation: stores decipher keys associated with respective portions ofcontent of the second memory area; executes a signature check on a firstportion of content of the second memory area, the first portion ofcontent storing data and instructions to implement a first operatingsystem; in response to the signature check on the first portion ofcontent verifying the first portion of content, sends a decipher keyassociated with the first portion of content to the microcontroller; andin response to the signature check on the first portion of content notverifying the first portion of content: executes a signature check on asecond portion of content of the second memory area, the second portionof content storing data and instructions to implement a second operatingsystem; and in response to the signature check on the second portion ofcontent verifying the second portion of content, sends a decipher keyassociated with the second portion of content to the microcontroller. 6.The electronic device according to claim 5, wherein the plurality ofportions of content of the second memory area store data andinstructions to implement respective operating systems of a plurality ofoperating systems.
 7. The electronic device according to claim 6,wherein the embedded secure circuit, in operation, responds to a failureof verification of a set of the plurality of portions by sending a dummydecipher key to the microcontroller.
 8. The electronic device accordingto claim 6, wherein embedded secure circuit, in operation, responds to afailure of verification of a set of the plurality of portions by sendingdata and instructions to cause the microcontroller to implement anoperating system other than one of the plurality of operating systems.9. The electronic device according to claim 6, wherein: themicrocontroller, in operation, generates a second key, and transmits thesecond key to the embedded secure circuit; and the embedded securecircuit, in operation, encrypts decipher keys using the second key,wherein the sending a decipher key to the microcontroller comprisessending an encrypted decipher key to the microcontroller.
 10. Anon-transitory computer-readable medium having contents which configurean electronic device to perform a method, the method comprising:starting a microcontroller of the electronic device with instructionsstored in a first memory area of the electronic device, wherein thefirst memory area is a secure memory area; starting a secure circuit ofthe electronic device, the secure circuit having a plurality of decipherkeys associated with respective portions of content of a second memoryarea of the electronic device, wherein the second memory area is anon-volatile memory area; executing, with the secure circuit, asignature check on a first portion of content of the second memory area,the first portion of content storing data and instructions to implementa first operating system; in response to the signature check verifyingthe first portion of content, sending, by the secure circuit, a decipherkey associated with the first portion of content to the microcontroller;and in response to the signature check not verifying the first portionof content, executing, by the secure circuit, a signature check of asecond portion of content of the second memory area, the second portionof content storing data and instructions to implement a second operatingsystem.
 11. The non-transitory computer-readable medium of claim 10,wherein the method comprises: generating, by the microcontroller, asecond key, and transmitting the second key to the secure circuit; andencrypting, by the secure circuit, the decipher key using the secondkey, wherein the sending the decipher key to the microcontrollercomprises sending the encrypted decipher key to the microcontroller. 12.The non-transitory computer-readable medium of claim 11, wherein thecontents comprise instructions executable by the secure circuit.
 13. Anelectronic device, comprising: a microcontroller; a first memory areaassociated with the microcontroller, wherein the first memory area is asecure memory area, which, in operation, stores instructions executableby the microcontroller; a second memory area associated with themicrocontroller, wherein the second memory area is a reprogrammablenon-volatile memory area having a plurality of portions of content; andan embedded secure circuit coupled to the microcontroller, the embeddedsecure circuit having decipher keys associated with respective portionsof the plurality of portions of of content of the second memory area,wherein the embedded secure circuit, in operation: executes a signaturecheck on a first portion of content of the plurality of portions ofcontent of the second memory area; in response to the signature checkverifying the first portion of content, sends a decipher key of theplurality of decipher keys which is associated with the first portion ofcontent to the microcontroller; and in response to the signature checknot verifying the first portion of content: selects another portion ofcontent of the plurality of portions of content of the second memoryarea to check based on an instruction received during a previousimplementation of a portion of content of the plurality of portions ofcontent of the second memory area; and executes a signature check of theanother portion of content of the plurality of portions of content ofthe second memory area.
 14. The electronic device according to claim 13,wherein the plurality of portions of content of the second memory areastore data and instructions to implement respective operating systems ofa plurality of operating systems.
 15. The electronic device according toclaim 14, wherein the embedded secure circuit, in operation, responds toa failure of verification of a set of the plurality of portions bysending a dummy decipher key to the microcontroller.
 16. The electronicdevice according to claim 14, wherein embedded secure circuit, inoperation, responds to a failure of verification of a set of theplurality of portions by sending data and instructions to cause themicrocontroller to implement an operating system other than one of theplurality of operating systems.
 17. The electonic device according toclaim 13, wherein: the microcontroller, in operation, generates a secondkey, and transmits the second key to the embedded secure circuit; andthe embedded secure circuit, in operation, encrypts the decipher keyusing the second key, wherein the sending the decipher key to themicrocontroller comprises sending the encrypted decipher key to themicrocontroller.
 18. An electronic device, comprising: amicrocontroller; a first memory area coupled to microcontroller, whereinthe first memory area is a secure memory area, which, in operation,stores instructions executable by the microcontroller; a second memoryarea coupled to the microcontroller; and an embedded secure circuitcoupled to the microcontroller, wherein: the microcontroller, inoperation: executes boot instructions stored in the first memory area;sends a start instruction to the embedded secure circuit; transmits afirst key to the embedded secure circuit; and responds to receipt of anencrpted decipher key from the embedded secure circuit by: decryptingthe encrypted decipher key; and deciphering a portion of content of thesecond memory area using the decrypted decipher key; and the embeddedsecure circuit, in operation: boots in response to the startinstruction; in response to receiving the first key, executes asignature check on a first portion of content of the second memory area;in response to the signature check on the first portion of contentverifying the first portion of content, encrypts a first decipher keyassociated with the first portion of content using the first key andsends the encrypted first decipher key to the microcontroller; and inresponse to the signature check on the first portion of content notverifying the first portion of content: executes a signature check on asecond portion of content of the second memory area; and in response tothe signature check on the second portion of content verifying thesecond portion of content, encrypts a second decipher key associatedwith the second portion of content using the first key and sends theencrypted second decipher key to the microcontroller.
 19. The electronicdevice according to claim 18, wherein the second memory area has aplurality of portions of content, which, in operation, store data andinstructions to implement respective operating systems of a plurality ofoperating systems.
 20. The electronic device according to claim 19,wherein the embedded secure circuit, in operation, responds to a failureof verification of a set of the plurality of portions of content bysending a dummy decipher key to the microcontroller.
 21. The electronicdevice according to claim 19, wherein embedded secure circuit, inoperation, responds to a failure of verification of a set of theplurality of portions of content by sending data and instructions tocause the microcontroller to implement an operating system other thanone of the plurality of operating systems.